Articulated joints must be permanently lubricated; such lubrication is provided by means of grease enclosed in a bellows sealing sheath surrounding the joint.
The amount of grease enclosed in the sealing sheaths at present provided is very high, of the order of 130 to 160 g for a universal joint situated at the side of the gear box of a medium price range vehicle. When the speed of the rotation of the joint is high, the centrifugal force exerted on the grease is high and has harmful effects on the sheath.
In order to reduce the amount of grease contained in the joint the dimensions of the sheath could be reduced, but the bellows would then be closer to the shafts connected together by the joints, which would involve a risk of abrasion. It has also be proposed to provide rings outside the sheath; but the problems of abrasion also arise in this case, since the rings rub against the bottom of the folds of the bellows.
French Pat. No. 1 465 613 describes a bellows sealing sheath including a bellows which connects together two sleeves intended to be mounted respectively on the driving element and on the driven element and which have an inner ring in the extension of the first fold at the side of one of the elements. This ring makes the joint rigid so that it withstands well the effects of the centrifugal force.